1. Field of the Invention
The present invention relates to an acceleration sensor for detecting acceleration acting on the sensor body, and, more particularly, to an acceleration sensor for detecting acceleration in the form of changes in the temperature distribution of gas in a closed space.
2. Description of the Related Art
Disclosed in Japanese Published Unexamined Patent Application No. 3-176669 is an acceleration sensor in which the equilibrium of the temperature distribution is formed by heating a gas enclosed in a closed space in a case, and the phenomenon in which the temperature distribution is changed while a gas flow is generated by the action of acceleration is detected as a change in the resistance of a resistance temperature sensor disposed within the case.
In the above conventional acceleration sensor, a thin-film-resistor temperature sensor serving as a heater is disposed in a resin case, and heated by applying current thereto. Resistance values are previously detected for the heated thin-film-resistor temperature sensor at various temperatures.
When acceleration acts on the acceleration sensor, a gas flow is generated in the case. The generated gas flow takes heat from the thin-film-resistor temperature sensor, thereby reducing its temperature so that the resistance of the thin-film-resistor temperature sensor is changed.
Because the change in the resistance of the thin-film-resistor temperature sensor corresponds to the acceleration acting on the acceleration sensor, the acceleration is detected by converting the resistance of the thin-film-resistor temperature sensor to an electric signal.
The conventional acceleration sensor has, however, a problem that, although it can detect the absolute value of acceleration, it cannot detect the direction in which acceleration acts because it uses a heater heating the gas in the case and a thin-film-resistor temperature sensor for the heater also serving as a temperature-sensing element which detects the temperature change due to the action of acceleration.
In addition, the conventional acceleration sensor has a problem that, because the thin-film-resistor temperature sensor for the heater serves as both a heater and a temperature-sensing element, aging from deterioration is caused in the thin-film-resistor temperature sensor for the heater if the generated temperature is high, leading to variations in heat generation and reduced sensitivity to temperature so that the sensor cannot accurately detect acceleration.
Moreover, the conventional acceleration sensor has a relatively bulky size for the closed space, which results in a degraded response to the temperature change by the gas flow. Reduction of the size of the acceleration sensor is limited by its structure.
Furthermore, while the accuracy of acceleration detection depends on the positional accuracy of the thin-film-resistor temperature sensor for the heater, the conventional acceleration sensor has a structure in which the thin-film-resistor temperature sensor for the heater is directly installed on the case, which makes it difficult to accurately position the thin-film-resistor temperature sensor for the heater.